1. Field of the Invention
The present invention relates to a hot-parison type injection stretch blow molding method and apparatus, which can continuously perform at least two steps of injection molding a preform (parison) and blow molding the preform into a hollow member through a single stage.
2. Description of the Related Art
One of such one-stage systems is disclosed in Japanese Patent Publication No. Sho 53-22096. This one-stage system comprises a machine base, four injection molding, temperature regulating, blow molding and ejecting stations located in the machine base on each side, and a rotating disc disposed above these working stations for intermittent rotation. The bottom of the rotating disc supports four neck molds, each for holding the neck of a preform or bottle. As the rotating disc is intermittently rotated through every 90 degrees, the four neck molds are circulatively carried in synchronism to the respective working stations. A series of successive steps are performed at the stations for forming a bottle. The time required at the injection molding station is the longest time required at any station. Hence, timing of intermittent rotation is determined according to the time required at the injection molding station. The injection molding time T includes clamping time, injection+cooling time and subsequent mold opening time. The intermittent rotation of the rotating disc is repeated at a time interval substantially equal to such an injection molding time T.
Japanese Patent Publication No. Sho 64-3657 discloses a linear conveyance type injection stretch blow molding system adapted to conveys neck molds along a loop-shaped conveyance path. For example, this linear conveyance type system comprises injection molding, temperature regulating and blow molding stations disposed in a lateral line and an ejecting station arranged in another line. As a preform is being injection molded at the injection molding station, the neck molds are moved between the other working stations in asynchronism with the injection molding cycle.
In the aforementioned systems, each of the neck molds is held by a neck mold support plate, which is circulatively conveyed through respective working stations. The rotary type blow molding machine requires neck mold support plates, which are equal in number to the stations. The linear conveyance type blow molding machine requires a number of neck mold support plates equal to or more than the working stations.
Usually, each of the neck molds used in such a one-stage type of blow molding system is also used as a neck cavity mold, which defines the outer neck wall of the preform in the injection molding station. The cavity mold is expensive since it requires a very high accuracy. Therefore, providing a number of neck molds equal to or more than the number of working stations, as in the prior art, increases the total cost of the molding system. With some types of moldings (vessels), blow molding time and/or temperature regulating time may be reduced or temperature regulating time may be omitted. In such a case, the molding system still requires the same number of neck mold support plates as the number of working stations for circulative conveyance. The neck mold support plate must be stopped unnecessarily in an omitted working station.